Rotary recliner mechanisms generally include of a first rotary member having a plurality of teeth and a second rotary member including one or more pawls adapted to lockingly engage the teeth to couple the rotary members to one another. Typically, one rotary member is mounted to a quadrant for attachment to a seat back and the second rotary member is mounted to a base plate for attachment to a seat base. The rotary recliner mechanisms are operable to lock the rotary member connected to the seat back to restrict its rotation, or to release the rotary member connected to the seat back to allow it to rotate and to enable the seat back to recline.
The rotary recliner mechanism is selectively locked or released by manipulating the one or more pawls, which are mounted for rotation between an engaged position where the teeth of the pawl and the teeth of the rotary member connected to the seat base mesh, and a disengaged position where the pawl retracts and no longer meshes with the teeth of the rotary member connected to the seat base. Locking rotary recliner mechanisms also may include a device, such as a spring, for releasably urging the pawl from the disengaged to the engaged position so that the default position for the mechanism is a locked condition. Further, the rotary recliner typically includes an activating mechanism that moves the pawl from the engaged position to the disengaged position.
In reclining seats, the seat back functions as an extremely long lever arm against which various forces are applied. The locking rotary recliner mechanism in a vehicle seat is relatively small compared to the length of the reclining seat back, and vehicle vibration or movement of an occupant may impose various forces upon that lever during use. These forces impose a large moment about the rotary member connected to the seat back when applied along such a lengthy lever arm. If the forces are sufficient, or the rotary recliner mechanism is poorly designed, these forces can overcome the capability of the rotary recliner mechanism to anchor the seat back.
In addition, any imperfection in the components of the pivot mechanisms, such as play or backlash between the engaging teeth or tolerances between the mechanism components, may allow the rotary member connected to the seat back to move a miniscule amount even when the mechanism is locked. These small movements are magnified by the length of the lever arm and become noticeable at the upper end of the seat. For example, the seat back of an unoccupied seat may tend to oscillate when the vehicle encounters rough road conditions. Because the motion of the seat back is amplified by the length of the seat back frame, the vibration of the seat back can be relatively large. This magnified play in locking pivot mechanisms has been termed “chucking” and refers to any imperfections or play in the mechanism components that allow movement of the rotary member and attached seat back while the mechanism is in a locked condition.
One technique employed to reduce chucking is to form the components of the pivot mechanism with exceedingly close tolerances. This technique reduces play in the mechanism, and thus reduces chucking, but manufacturing to such close tolerance is expensive. Further, close tolerances may bind the components of the system and prevent smooth operation.